.3 G Harq Principle Study, The Combination Of Decoding Algorithm

In order to improve the transmission reliability of data and image in 3G, the channel coding technology-HARQ combined by ARQ and FEC is often adapted widely. HARQ belongs to the link adaptive technology, which is the core to realize the HSDPA proposed by 3GPP.This paper provides the coding schemes of HARQ and the protocols of limited times packet retransmission. Especially, the analysis of performance and the mechanism of operation of the N-channel stop-and-wait protocol are given in detail. In the result, the mechanism of operation of the N-channel stop-and-wait protocol is simple and the payoff of signaling is small. With the increasing of the number of parallel channels, the throughput of system can be improved and the transmission delay can be decreased. At the same time, the buffer of the receiver can be also reduced.This paper focuses on the discussion of the combining decoding algorithm on retransmission packets. A new combining decoding algorithm is proposed and the advantages over the Chase combining algorithm is demonstrated. The computer simulations show that the HARQ with the new combining decoding algorithm is obviously superior to the HARQ without the combining algorithm and also a rather advantage over the HARQ with traditional Chase combining decoding algorithm in terms of the number of retransmissions and the throughput of system. For example, the average number of retransmissions can be decreased 50% at 1 dB SNR in the Gaussian channel and 9 dB SNR in the Rayleigh channel.